Additional observations on the mystery plant
The mystery plant showed etiolated symptom, due to light deprivation. How-ever the leaves consistently showing opposite pair attachment on stem, both on old stem (red circle) and young etiolated stem (yellow circles).
The stem has articulate joint with rings/line, at the leave's attachment level (green circle). It also branched in opposite manner. All of these are not consistent with Portulacas, but consistent with some (but not all) Pileas.
Most Pileas species will have opposite leaves. Most with jointed stems.
The mystery plant shows some opposite paired leaves, but there are also whorled of three leaves at few segments.
The venation on the leaves are not clearly shown, but vaguely there are two parallel larger secondary veins, creating "Forking appearance". This type of venation can be found in some Pilea, but not in Portulacas
The veins are subtle, but if carefully observed, it is there.
here is an image from
https://peaceloveandhappiness.... showing the veins vaguely
For comparison to Portulaca, especially P umbraticola; below pictures are from the garden.org database
Portulaca umbraticola leaves can seems opposite especially on compact plant, but they are not true opposite leaved plant. Leaves actually are alternate. The branching are alternate (very rarely opposite), there are no joints or rings on stem.
Portulaca umbraticola when etiolated will show "alternate" leaves arrangement even better, few leaves near the tip can still be opposite or sub-opposite, but these will morph into "alternate" as the stem elongated due to etiolation. This phenomenon shows it's is not a true opposite-leaved plant.
The veins on leaves are difficult to observes but they do not have forking appearance.
Those are some of the observation that lead me to lean on Pilea especially Pilea glauca / Pilea libanensis
